Cathode ray harmonic filter



Dec. 27, 1955 K. F. Ross 2,7288'54 CATHODE RAY HARMONIC FILTER FiledApril 11,-1950 fig. j

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INVENTOR.-`

G LZ) 6 02 y, nella f "gf ma United States Patentrce 2,728,854 CATHODERAY HARMONIC FILTER Karl F. Ross, Bronx, N. Y.

`Application April 11, 1950, Serial No. 155,205

3 Claims. (Cl. Z50-27) My invention relates toa harmonic filter forelectro magnetic waves.

An object of this invention is to provide a harmonic filter designed forwaves of high frequency and adapted to be conveniently and continuouslyadjusted for a displacement of its pass and stop bands Within widefrequency limits.

Another object of the present invention is to provide a filter of thecharacter described wherein the positions. of the pass and stop bandsmay be instantaneously interchanged. p

A further object of this invention is to provide afrequencydiscriminator with very sharp cutoff effective where only a singlefrequency is received.

Still another object of the invention, allied with the preceding one, isto provide a discriminator which will substantially reject all incomingwaves except a single, pure sine wave of predetermined frequency.

Yet a further object of the instant invention, .allied with the oneimmediately preceding, is to provide a frequency discriminator whichwill also distinguish between pure sine waves of the desired frequencybut of different amplitudes and which may be used as a means forseparately utilizing or for selectively channeling such waves ofdifferent amplitudes.

lt is also an object of my invention to provide, in a cathode ray tube,a novel type of output electrode adapted to be used in a filter of thecharacter set forth above.

` The invention will be described with reference to the accompanyingdrawing wherein:

Figs. 1 and 2 are two circuit arrangements representing differentembodiments of the inventiom'and Figs. 3 through 7 show different outputelectrodes usable with the arrangement of Fig. 2.

Throughout the drawing, similar elements have been denoted by the samereference numerals prefixed by different hundreds digits identifying therespective figure.

Referring to Fig. l, thereis shown va cathode ray tube 100 comprising asource of electrons's'hown as a cathode 101 and focusing or beam formingmeans shown as a first anode 102 and a second or accelerating anode 103.The electrodes 101, 102 and 103 derive their potentials from a battery104 and a potentiometer 105 in series therewith.

Two pairs of deflecting electrodes 106', 106" and 107, 107", botharranged in the same plane (assumed to be the vertical plane of symmetryof the tube 100), receive signals from input terminals S', 108" to whichthe electrodes 106', 106" are connected directly and the electrodes107', 107", which are axially spaced from the former, by way of a switch109 and a delay network 110. Network 110 may consist of one or morelow-pass filter sections, dependingupon the amount of phase shiftdesired, and has been shown as consisting of two such sections, thusgiving a phase shift ranging from zero to 360 within the pass bandthereof which is the only range of frequencies of interest in thisconnection; j v

` The beam 111, produced by the electron gun 101- 103, impinges upon anoutput electrode generally indicated at Patented Dec. 27, 1955 112 andconsisting of a dielectric backing 113, a layer 114 of resistancematerial thereon and a pair of highly conductive terminal members 115',115" in contact with J that layer at respective ends thereof. Other usesfor an electrode of this description have been disclosed in co pendingapplication Ser. No. 155,207, by Phil Cutler and Karl F. Ross, filed oneven date herewith.

The terminal members 115', 115" are connected across an output resistor116, grounded at its center, and to respective output terminals 117',117".

j The operation of the system of Fig. l is as follows:

Waves of different frequencies and amplitudes are applied to the inputterminals 108', 108" and, thereby, to the electrodes 106', 106", thusdeflecting the beam 111 in a vertical sweep dependent in its extentrupon the-'instantaneous amplitude of the combined signal. Assumf ingthe switch 109 to be open, the beam will produce an output at terminals117', 117" which will be substantially proportional to the input signal;this will be understood by considering the elements 114, 116 as the fourarms of a Wheatstone bridge the four corners of which are given by theterminals 117', 117", the grounded center of resistor 116 and the pointof impingement of the beam 111 upon the resistive layer 114. Thus acentering of the beam with respect to electrode 112 will causev theelectrons to flow to ground in equal amounts via the upper and the lowerhalf of resistor 116, resulting in a.y zero output signal, whereasdeflection of the beam in one j sense or the other will impress avoltage of correspond ing polarity upon the terminals 117', 117". Thesystem of Fig. l will then function as an amplifier and/or as a delaydevice the delay of which may be varied by changing the velocity of theelectrons of the beam, as by displacing the slider of acceleratingelectrode 103 on potentiometer 105.

When the switch 109 is closed, the beam 111 will be,`

subjected to an additional deflection by means of the electrodes 107',107". When the frequency of the incomingV wave is such that its phaseshift in the network is zero, 360 or any other Whole number of fullcyclesth e deflecting voltages on electrodes 106', 106" and 107', 107"`will be in phase, so that the angle of deflection of the beam 111 willbe increased as shown at 111a, this in turn resulting in an increase inthe amplitude of the output signal. When the frequency of the incomingwave is such that its phase shift in the network 110 is 180 or any otherodd number of half cycles, the deecting volti ages will b e in phaseopposition resulting, with proper" substantially suppress frequenciesfor which the phase' shift in network 110 is an odd number of halfcyclesV while greatly amplifying those for which ythis shift is a wholenumber of cycles. The system of Fig. 1 may be modified by the additionof a switch permitting reversal of the connections between Adeflectingelectrodes 106',

106" and 107', 107", so asv to enable the filter to pass thefirst-mentioned group of frequencies while suppressing thelast-mentioned ones; also, the delay network 110 may be omitted and thetraveling time of the electrons in the suitably lengthened tube reliedon to introduce the necessary delay.. Both of these features have beenillus-V trated in Fig. 2.

In Fig. 2 the tube has been indicated at zo'athe inputterminals at 208,208" and the output electrode, several 5 thus allowing the tube 200 tobe of cylindrical configura-- tion, A reversing switch 218 connectsthese electrodes and the input terminals 208', 208" to the second set ofdeecting electrodes, 217', 217", which the electrons of the beam 211reach after traversing -a length of tube which in the following shall bevdesignated L.

.it will be noted that, in contradistinction to the arrangement' of Fig.1, the second set of deflecting electrodes 217', 2117" is positioned atright angles to the first set'- 216a' etc. Assuming that the spacing ofoutput electrode 212 from the second set of deflecting electrodes issuch thatY a signal of given intensity will produce the same amount ofvertical and of horizontal deflection of the beam 211 at electrode 212,then signal wavesv of different frequencies will produce traces oflinear, elliptical and circular configuration as illustrated in Fig. 3.

ln Fig. 3 there is shown an output electrode 312 having the form of aninclined square, or diamond, this electrodefcornprising a resistivelayer 314 and conductive terminal strips 315', 315" as well as,preferably, a dielectric backing such as element 113 in Fig. l. Anoutput -resistor 316, grounded at its center, and output terminals 317',317" are connected across the strips 315', 315" which are inclined at anangle of 45" to the horizontal.

-Let f 'be the `frequency of the incoming wave, v the speed of theelectrons, t=1/f the period of oscillation and T :L/ v the timenecessary for the electrons to traverse the distance L. Let us alsoassume that the switch 218 is in its right-hand position, so that thevoltage on horizontal deecting electrode 217 (the right-hand electrodewhen viewed in the direction of electron travel) and on verticaldeflecting electrode 21611" (the upper electrode of the pair determiningthe sense of vertical deflection) is the same.

If for a given frequency f1=1/t1 the time T is equal to or is anintegral multiple of tl, then it can be easily shown 'that under theassumed conditions the locus of impingement of the beam 112 will be aline extending at right angles to the strips 315', 315, this will betrue for all the frequencies for which fl=v/L, Zv/L, 3v/L etc.Similarly, for the frequencies f2=v/2L, 3v/2L, 5v./2L etc. .the locus ofimpingement will be a line at right angles to the one referred to, thuslparallel to the stripsr315, 315". For f3=.v/4L, 3v/4L, 5v/4L etc. thelocus will be a circle; for #tsv/8L, 7v/8L, 9v/8L, lSv/SL, 17V/8L ete.and neighboring values it will be an ellipse having its major axisextending at right angles to the strips 315', 315"; and for f5=3v/8L,5v/8L, liv/8L, 13v/8L, 19V/8L etc. and neighboring values it will be .anellipse having its major axis extending parallel to these strips. All ofthese traces have been illustrated in Fig. 3 at fl f5, respectively. p

'lt will now be `apparent that a sweep of the beam kat right angles Itothe terminal strips 315', 315 will result in'a maximum signal at outputterminals 317', 317" while asweep parallel thereto will have no effectWhatsoever. Thus each frequency will contributeto the output signal onlyto the extent that its trace on the electrode 312 has -a componentperpendicular to the strips'315, 315". These components are a maximumfor frequencies fl,- are'progressively smaller for frequencies f4, f3'and f5 and disappear entirely for the frequencies f2. Thustherefh'a-s-again been provided n harmonic filter whose passfbands`vr(centered on fl) and stop bands (centered onfZ) may be readily variedby changing` the speed of.

quencies ,previously passed and will transmit those pretit viouslyattenuated.

it will also be understood-that the spacing between pass or stop bandsmay be increased and the bands more sharply deli-ned by cascading aplurality of filters of the type disclosed, with the value of v/Lincreasing or decreasing for successive filters according to a binaryprogression.

'l'he remaining figures show electrodes adapted for use with systemsdesigned to discriminate between a single, pure sine wave ofpredetermined frequency, on the one hand, and other types of waves,`including or not including, the desired frequency, on the other. Suchdevices are particularly useful in voice frequency signaling vsystems oftelephone circuits wherein it is necessary to guard against falseoperation of a relay or other switching device by speech waves thathappen to include the critical frequency. Referring to Fig. 4, vthereare shown three concentric ring electrodes of highly conductivematerial, indicated at 41211, 41219 and 412C, respectively. Each ofthese electrodes is connected to a respective output resistor 416:1,41615, 416e and a respective output terminal 417a", 4171;", 417C", thelatter in turn being connected to grounded terminal 417' by way ofrespective condensers 4i9a, 419b, 419e.

lt will now be seen that the arrival of a wave consisting of a pure sinewave of frequency f3 will cause the beam to trace a circular path which,depending upon the amplitude of the wave, maybe made to coincide withone of the electrodes 416:1, Iiltb, 416C, thus giving rise to a D.-C.output signal at the corresponding set of terminals. lf the frequency ofthe Wave has any value other than those listed under the group f3, thebeam will only intermittently intersect the electrodes of Fig. 4, thusproducing a series of short pulses which will be ineffective to resultin any switching operation, being largely shunted to ground through therespective condensers 419a, 419b, and 419C. A similar situation willexist if some other signal is superimposed upon the wave of frequencyf3, since then the trace will be displaced .from its concentric positionwith respect toA the electrodes 412a, 412b and L,llZc.

Fig. 5 shows a single electrode 512 consisting of .a conductive stripinclined at an angleV of 45 to the horizontal and connected to an outputresistor 516, the .output terminals 517', 517" being bridged byacondenser From the foregoing it will be understood Vthat'this electroderesponds only to a Wave of frequency f2 and substantially rejects allother types of waves. In Vthis case the output signal appearing .at thevterminals 517', 5,17" will be independent of the amplitude of theincoming wave.. v

Fig. 6 shows three concentric electrodes 612a, 6121), 612C similar tothe electrodes of Fig. 4 but comprising lrespective annular layers614:1, 614b, 614C of resistance' material and pairs of diametricallyopposite terminal eleof these .terminal elements is grounded by way of aYrespective output resistor Md-616e' and 616a"-616c",

shunted by a respective condenser 619a-`619c and 6'19a"-619c". Thecorresponding output terminals are indicated at 617a'--617c' and617a"-617c".

of the .incoming-wave, rather than ,a D.C. potential. The arrangement ofFig. 6 may, accordingly, be used as a means for individually channelingsignal waves of given frequency but different amplitude.

The arrangement of Fig. 7 is similar to that of Fig. 5 in that itcomprises a single electrode 712, inclined Aat an angle of 45. Thiselectrode is, however, of a construction analogous to that of electrode112 in Fig. 1, comprising a resistive layer 714 and terminal elements715', 715". Each of these terminal elements is grounded by way of aresistor 716', 716" bridged by a condenser 719', 719", respectively,these terminal elements being further connected to output terminals717', 717".

The system of Fig. 7 will thus reproduce a wave of frequency f2 togetherwith any amplitude variations thereof and may be used in combinationwith a selective repeater or amplifier for such a wave.

It is to be understood that my invention is not limited to the specificembodiments described and illustrated and that various modications andadaptations are possible without exceeding its'scope. Thus it will beapparent, for example, that delay means other than thosel specicallyshown may be used in connection therewith, such as, for example, liquiddelay lines, transmission lines and the like; also, the electrodesdiscussed in connection with Figs. 4-7 may be moded to conform, say, tosome other of the traces adapted to be described by the beam, e. g.those shown at f4 or f5 in Fig. 3.

The specific electrode configurations shown in Figs. 3-7 have not beenclaimed in the present patent but, insofar as they appear to be novel,are claimed in my co-pending application Ser. No. 511,627, led May 27,1955.

I claim:

1. A wave ilter comprising a source of electrons, focusing means formingsaid electrons into a beam, a source of signal waves, rst and seconddeecting means positioned along the path of said beam with a spacingsuch that the transit time for beam electrons between said two deectingmeans is at least a substantial fraction of an oscillatory period ofsaid signal waves, circuit means applying Waves from said source ofsignal waves to both of said deflecting means with a substantiallyfrequency independent relative phasing yet with relatively dephaseddelecting effects upon said beam, the dephasing of said deilectingelects being due to said transit time and varying with the frequency ofsaid signal waves, and target means in the path of said beam shaped andpositioned to respond to a deflection of said beam in a direction inReferences Cited in the le of this patent UNITED STATES PATENTS1,882,850 Marrison Oct. 18, 1932 1,999,884 Salzberg Apr. 30, 19352,118,867 Schlesinger May 31, 1938 2,124,973 Fearing July 26, 19382,182,382 Hollmann Dec. 5, 1939 2,239,407 Wagner Apr. 22, 1941 2,263,376Blumlein Nov. 18, 1941 2,289,319 Stobel July 7, 1942 2,326,877 MuellerAug. 17, 1943 2,374,666 Cunnil May 1, 1945 2,376,707 McCoy May 22, 19452,404,106 Snyder, Jr. July 16, 1946 2,431,488 Larson Nov. 25, 19472,449,975 Bishop et al Sept. 28, 1948 2,477,547 Rggen July 26, 19492,507,590 Clark May 16, 1950 2,617,078 Van Overbeek Nov. 4, 1952

